1. Field of the Invention
The present invention relates to a controlling apparatus for a continuously variable transmission which changes a speed-change ratio so that an actual rotation speed of an input shaft of the continuously variable transmission coincides with a target rotation speed thereof. In particular, it relates to setting of the target rotation speed upon a vehicle regular running.
2. Description of Related Art
In a vehicle equipped with a continuously variable transmission, a drive force of a power source for running is speed-changed at the continuously variable transmission, and then is transmitted to drive wheels. A target driving force of the drive wheels is set based on an accelerator operation amount and the like, and a target rotation speed of an input shaft of the continuously variable transmission is set based thereon. Then, a speed-change ratio of the continuously variable transmission is controlled by a controlling apparatus so that an actual rotation speed of the input shaft coincides with the above target rotation speed.
A patent document (Japanese Patent Application Laid-open No. 2001-330133) has disclosed an example of such controlling apparatus for the continuously variable transmission apparatus. According to this controlling apparatus, the target drive force for keeping a vehicle speed constant is calculated, and an imaginary throttle open-degree is obtained based thereon by a map. Then, based on the vehicle speed and the imaginary throttle open degree, the target rotation speed of the input shaft is calculated by a speed-change map, whereby the continuously variable transmission is speed-changed.
By the way, the power source for running (for example, engine) is also used for driving an auxiliary machine of the vehicle such as a compressor for air-conditioner. In this case, the above mentioned target drive force is calculated by taking the load required for driving the auxiliary machine into consideration to secure a suitable operation of the auxiliary machine. Accordingly, the target driving force may fluctuate depending on the operating condition i.e., a load of the auxiliary machine, so that the target rotation speed of the continuously variable transmission calculated based on the target driving force may also fluctuate to thereby fluctuate the actual rotation speed. Thus, fluctuation of the actual rotation speed may cause an unexpected fluctuation of the rotation speed of the engine upon a vehicle regular running wherein the vehicle runs, for example, at the constant vehicle speed. In this way, a drivability of the vehicle may be worsened.